Copper plated Crossman BBs are also known to work well for fuel tank clean up. These, being smaller in diameter and less pointy will tend to get into the corners and nooks and crannies a little better. If the sediment and rust is bad, the bolts and nuts will work faster.
Keep in mind that Coleman used an internal swish solution at the factory for rust prevention, which can sometimes look like surface rust, given its pinkish hue. More than one person has gone through the effort to remove this factory rust preventative film thinking it was the start of something bad. Here's a pic of the surface finish in a lantern, but you get the idea. Pretty sure they used this on stove tanks, too.
Keep in mind that Coleman used an internal swish solution at the factory for rust prevention, which can sometimes look like surface rust, given its pinkish hue. More than one person has gone through the effort to remove this factory rust preventative film thinking it was the start of something bad. Here's a pic of the surface finish in a lantern, but you get the idea. Pretty sure they used this on stove tanks, too.